Thermal analyses of TN-24P dry storage cask with heterogeneous fuel assembly modeling

The wet storage capacity of used nuclear fuels (UNFs) in South Korea is expected to reach a saturation point within a few years. Dry storage of UNFs is required, and thermal safety analysis of UNFs in a dry storage cask is therefore necessary. From this standpoint, the thermal evaluations of the TN-24P cask were conducted in this study. The UNF geometries were heterogeneously composed of many fuel rods. Thermal evaluations were conducted for backfill gas conditions through simulations that were coupled with heat transfer and fluid flow. In addition, another thermal evaluation was conducted under vacuum conditions through a simulation involving heat transfer only. The maximum temperatures for the helium, nitrogen, and vacuum backfill conditions were recorded at axial locations above the center, near the top, and at the center of the fuels, respectively. The highest maximum temperature was recorded in the vacuum backfill condition, followed by the second highest temperature in the nitrogen backfill and the third highest temperature in the helium backfill condition. Moreover, the simulation results agreed well with the measured data. The maximum temperatures for the three simulations did not exceed 400 degrees C; thus, all evaluations of the cask met the acceptable criteria for dry storage. However, the simulation results were significantly affected by the gas pressure in the helium backfill condition and the thermal conductivity of the basket in the vacuum condition.